Extensometers are instruments for measuring a change in elongation of a specimen under a stretching force. Thus in materials analysis, it is oftentimes desirable to know precisely the percent elongation of a member prior to rupture as well as the rupturing force.
Generally, it is desirable to provide a continuous direct read-out of the specimen elongation during a test. Towards this end, the more recently developed extensometers provide strain gage flexure means responsive to elongation of the specimen to provide an electrical signal from a strain gage bridge which may be properly calibrated to indicate the elongation. Typical extensometers of this type will include a pair of leg elements which can be secured at spaced points to the specimen under test, separation of the securement points of the legs as the specimen stretches providing flexure action which is measured by the strain gages in the device. U.S. Pat. No. 3,319,338 issued on May 16, 1967 illustrates a typical extensometer of this type.
In utilizing such extensometers, separate securing means are provided for securing the ends of each of the legs to spaced points on a specimen. The actual attachment of the extensometers as are presently available is somewhat awkward and time consuming in view of this particular type of design utilizing the separate securing elements. Moreover, care must be exercised to secure the ends of the legs at precisely spaced points on the specimen as otherwise a proper reference is not provided for measuring the elongation.
Finally, when more than one extensometer is being used for different gage lengths or different percents of maximum strain, no provisions have been made to allow for interchangeability between different extensometers and one recording instrument. It would be desirable to provide an extensometer which can accommodate different type specimens wherein different percentage elongations are to be indicated and yet wherein the flexure portions utilizing strain gages is always flexed a constant amount.